If the librarian doesn't cancel your book when you return it, there may be no record in the system. You should go to the stacks to find the books you returned. Generally speaking, the system does not support borrowing your books without cancellation. Your book should still be in the library (if no one stole it illegally). Look for it in a fixed position according to the bar code, and don't forget to turn it on the bookshelf.
If it still doesn't work, you can go to the leader. This problem is the responsibility of the library, and the leader should not be difficult for you.
Finally, I suggest you complain, but I don't suggest you borrow books without paying back the mortgage.